The present application relates generally to an improved structure for enhancing reference return current conduction. More specifically, the present invention is directed to such a structure employed in printed wiring cards employing blind/buried vias.
High signaling rates and large numbers of wide busses are required in today's computing devices, e.g., server computing devices. Such is required in order to transfer data and commands between different subsystems and take full advantage of the processing capabilities of the computing device. In order to accommodate the number of signals and the large collection of interconnections, printed wiring boards have become more complex.
A printed wiring board (PWB), also known as a printed circuit board (PCB) or etched wiring board, is a board that is used to mechanically support and electrically connect electronic components using conductive pathways, tracks, or traces etched from sheets of conductive material laminated onto a non-conductive substrate. A PWB or PCB populated with electronic components is a printed circuit assembly (PCA) or printed circuit board assembly (PCBA). PCBs are inexpensive and generally highly reliable.
Complex technologies have been introduced and utilized in PWBs or PCBs in order to accommodate the signaling and interconnection requirements of modern computing devices. Typically, vias are used in such structures to provide interconnection between layers of the PWBs or PCBs. Vias are pads with plated holes that provide electrical connections between conductive pathways, tracks, or traces on different layers of the PWB or PCB. The holes are made conductive by electroplating, or are filled with annular rings or small rivets. High density multi-layer PWBs or PCBs may have micro-vias.
There are three basic types of vias or micro-vias used for these purposes. A first type of via is the through via which is drilled through the finished laminated card structure. A second type of via is a blind via which has one end of the via exposed to the surface of the card and the other side terminated within the card stack-up of layers. A third type of via is the buried via which has both ends of the via being not exposed to the surface of the card.
One class of complex technology that has been introduced is the use of blind/buried (BB) vias. In one implementation, the blind/buried vias are formed by laminating sub-composites together, each sub-composite employing small quantities of layers and using through hole via technologies, either laser or mechanically drilled, for the sub-composites. That is, a blind via is formed in a sub-composite of the laminated card structure and then is subsequently overlaid with another sub-composite causing the blind via to become buried within the laminated card structure. The resulting vias turn out to be blind/buried (BB) when the complete card is laminated together with the sub-composites stacking up on top of each other. These BB vias and the interconnects they form do not interfere with routing on other sub-composites. As a result, denser wiring is accommodated as compared to a traditional printed circuit process utilizing only plated through holes (PTHs).